Arcing time relay

ABSTRACT

An arcing time relay is provided for vacuum circuit breakers, and measures the length of time that arcing occurs after the circuit breaker contacts are open, or measures the time that excessive leakage current flows while the contacts are open, and provides an output signal if arcing time or leakage current exceeds given bounds which indicate improper vacuum conditions.

United States Patent 91 May [451 May 22, 1973 ARCING TIME RELAY [56]References Cited [75] Inventor: William E. May, Levittown, Pa. I UNITEDSTATES PATENTS [73] Assignee: I-T-E Imperial Corporation, 3,431,431 3/1969 Martin ..3l7/ 11 R Philadelphia, Pa. 3,641,359 2/ 1972 McCarty..307/l36 [22] Filed: July 18, 1972 Primary Examiner-James D. TrammellAttorney-Sidney G. Faber Bernard Gerb, Marvin 21 A LN ..272724 1 pp 0 C.Soffen et al.

52 US. Cl. ..317/11 R, 307/136, 317/27 R, [57] ABSTRACT 317/33 R, 317/36TD, 317/46, 317/62, An arcing time relay is provided for vacuum circuit340/253 R breakers, and measures the length of time that arcing [51]Int. Cl. ..l-l02h 7/22 occurs after the circuit breaker contacts areopen, or [58] Field of Search ..317/27 R, 36 TD, measures the time thatexcessive leakage current flows 317/11 R, 62, 33 R, 46; 307/136; 340/253R while the contacts are open, and provides an output signal if arcingtime or leakage current exceeds given bounds which indicate impropervacuum conditions.

Patented May 22, 1973 2 Sheets-Sheet Patented May 22, 1973 2Sheets-Sheet 2 ARCING TIME RELAY BACKGROUND OF THE INVENTION Thisinvention relates to solid state relays, and more specifically to arelay which produces an output signal in response to extended circuitbreaker arcing time or leakage current flow while the circuit breakercontacts are open.

While the invention may be applied to any type of circuit breaker, it isparticularly applicable to circuit breakers using vacuum interrupters.In commercially available vacuum interrupters, a pair of butt contactswhich are relatively movable are enclosed in a sealed envelope which isevacuated to a hard vacuum. It is, however, possible that air can leakinto the vacuum due to mechanical failure, aging, defective materials,or the like, with the loss of vacuum taking place slowly andunnoticeably. As the vacuum is lost, the operational ability of thevacuum interrupter and its interrupting ability decreases, and can leadto unexpected failure of the circuit breaker. The loss of vacuum can bedetermined by an increase in arcing time, or the length of time takenfor the interrupter to clear a fault.

The failure of the vacuum beyond a given value may occur while thebreaker is standing open. This could cause a flashover of the contacts,due to decreased dielectric strength between them, so that a circuit isestablished through the open breaker contacts. Such failures areextremely dangerous and could cause serious personnel and propertydamage.

BRIEF SUMMARY OF THE INVENTION In accordance with the present invention,a highsensitivity relay is connected to the standard currenttransformers which are conventionally provided with high power circuitbreakers to monitor the current through each phase of a circuit breaker.The relay device is a completely solid state device and contains apickup circuit which delivers its signal through the conventional abreaker contact, which is the contact which is closed when the breakeris opened. Thus, a signal can be delivered through the a breakercontacts only beginning with the instant that the breaker contacts openor while they have been standing in an open position.

The a breaker contact signal, which can be derived from any phase of thebreaker, may be combined with the signals from other a breaker contactsof other breakers in a local system and this output signal is thenamplified and applied to a time delay circuit. Thus, if arcing current,which begins to flow with the opening of the contacts, lasts for longerthan some preset time in any phase being monitored, the common timedelay circuit will produce an output to operate a trip circuit or alarmcircuit. Similarly, if leakage current begins to flow while the breakeris standing open due to a defective vacuum in any phase, and thiscurrent flows for a given length of time, the time delay will similarlydevelop an output to actuate an alarm circuit or to trip a backupbreaker.

It will be noted that the present invention does not affect the normalelectromechanical relay operation of the relays conventionally connectedto the current transformers, since the relay of the invention has anextremely high input impedance. Thus, the novel relay of the inventioncan be easily attached to existing circuit breaker installations inorder to monitor the vacuum condition of the vacuum interrupters.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic block diagram ofthe circuit of the present invention.

FIG. 2 is a circuit diagram of one circuit which can carry out thefunctions illustrated in FIG. 1.

FIG. 3 is a modified diagram of the circuit shown in FIG. 2, wherein thecircuit contains a modified faultcurrent protection circuit from thatshown in FIG. 2.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring first toFIG. 1, the novel arcing time relay is shown in connection with athree-phase circuit breaker in which each circuit breaker pole includesa vacuum interrupter 10, 11 and 12, respectively. Note, however, thatthe invention is also applicable to any type of circuit breaker, wherearcing time must be closely monitored.

Each of the vacuum interrupters 10, 11 and 12 are connected in a phasewhich contains a conventional current transformer or other suitablecurrent monitoring device. By way of example, the phase containinginterrupter 10 has a conventional current transformer 13 which has agrounded burden resistor 14. Any other type of signal pickup circuitcould also be provided. By way of example, it is possible to place amagnetic core on a circuit which carries current from the currenttransformer output to an overcurrent relay which would commonly beprovided in the protective circuit of the breaker. The input of thearcing time relay is then ma netically coupled to the current flow tothe overcurrent relay, so that the input of the arcing time relay willbe unaffected by tap and time settings for the overcurrent relay whichmight affect the operation of the arcing time relay when the pickup istaken from the burden resistor 14.

The output of the burden resistor 14 serves as the input to the relay ofthe invention, and is initially connected to a fault current protectioncircuit 15. This circuit is needed since the relay of the presentinvention is to monitor extremely small currents. Therefore, it ispossible that the relay could be damaged by the relatively high outputsignal of the current transformer under fault current conditions. Thus,the fault current protection circuit 15 limits relay output currentunder fault current conditions.

The output of fault current protection circuit 15 is then connected tooperational amplifier 16 which is, in turn, connected to a dualcomparator circuit 17. The dual comparator circuit 17 is a commerciallyavailable integrated circuit type device which operates to produce asmall positive output when the output of the amplifier l6 deviates bysome given value from a given steady state signal level. In the case ofthe relay of the invention, the steady state level is selected to be atzero current. The output of dual comparator 17 is applied to oneterminal of an OR gate 18. The OR gate 18 has two additional inputswhich are derived from the phase pickup circuits associated with thephases containing vacuum interrupters l1 and 12, which circuitry will beidentical to the circuitry described above and which included components13, l4, l5, l6 and 17. Thus, an output is produced from the OR gate 18if a low current signal appears for either of the phases includinginterrupters 10, 11 and 12.

The output of OR gate 18 is then connected to the a breaker contact 19of the circuit breaker which contains interrupters 10, 11 and 12. The abreaker contact of a circuit breaker is the contact conventionally usedfor relaying purposes,-which contact is closed the instant theinterrupter contacts separate, and which is opened the instantinterrupter contacts close. Thus, so long as the interrupter contacts10, 11 and 12 are closed, the a breaker contact 19 is open so that nosignal passes through the remainder of the relay circuit.

In accordance with one feature of the invention, the remainder of therelay circuit could serve a common function for a group of circuitbreakers. Thus, further a breaker contacts 20 and 21, of other vacuumcircuit breakers being monitored, may be provided with input terminals22 and 23, respectively, which are, in turn, connected to respectivegroups of phase pickup circuits associated with these other breakers.

The output of the a breaker contacts including contact 19 is thenconnected to an amplifier 24, and the output of amplifier 24 is filteredin filter 25 and again amplified in amplifier 26. The output ofamplifier 26 is then connected to a suitable time delay circuit 27,which produces an increasing output with time so long as current flowsfrom amplifier 26. Note that a signal current output is applied to timedelay circuit 27 only when current continues to flow through anyinterrupter contact after the interrupter contact has opened. That is,the opening of the interrupter contacts closes its respective a breakercontact 19, 20 or 21 to permit transmission of a signal to time delaycircuit 27.

If the current flow in time delay 27 exceeds a given value after somegiven length of time, the output signal of time delay 27 reaches asufficiently high value to switch a Schmidt trigger circuit 28, whichcan, in turn, actuate a trip circuit of a backup breaker or an alarmcircuit 29. Thus, if the arcing time of any interrupter is greater thansome given value, due to vacuum leakage or some other problem, arcingcurrent will flow long enough to cause actuation of time delay 27, andthus the operation of an alarm circuit or the tripping of a backupbreaker by the trip or alarm circuit 29. Similarly, if, while thecontacts of the interrupter stand open, a current greater than somegiven value begins to and/or continues to flow, the time delay circuit27 will also operate Schmidt trigger 28 to produce an alarm and/ortripping of an appropriate backup breaker.

FIG. 2 is a detailed circuit diagram of one circuit which can producethe desired results described in connection with FIG. 1. Referring nowto FIG. 2, there is illustrated a current transformer input terminal 40,which corresponds to the input from burden resistor 14 in FIG. 1. Thecircuit of FIG. 2 is also provided with a source of positive biasingvoltage V+ connected at terminals 41, which provides the biasingvoltages for the relay circuit. The current transformer signal is thenconnected through resistor 42 and capacitor 43 to the input terminal ofoperational amplifier 44 (corresponding to operational amplifier 16 ofFIG. 1). Note that resistors 45 and 46 set the d-c bias level to whichis added the current transformer input signal from terminal 40.

Since the relay must be sensitive to the lowest possible currenttransformer primary current, it is necessary to protect the operationalamplifier 44 from the higher voltages associated with fault levelcurrent. To this end a fault current protection circuit (circuit ofFIG. 1) is provided, which includes transistors 47 and 48,

which are associated with biasing resistors 49, 50, 51 and 52.Transistor 47 is a PNP transistor and its emitter is biased slightlybelow the level set by resistors 45 and 46. The emitter of transistor48, which is an NPN transistor, is biased slightly above this samelevel. The bases of transistors 47 and 48 are then connected to theinput of operational amplifier 44. Thus, whenever the input signal fromterminal 40 goes above or below the biasing levels set by resistors49-50 or 51-52, respectively, either transistor 47 or transistor 48conducts to reduce the input signal to operational amplifier 44.

The output signal of operational amplifier 44 is connected to anintegrated circuit structure 60, which defines a dual comparator device(shown as comparator 17 in FIG. 1). This circuit separately compares twoinputs with two references and if either input exceeds its reference,the output voltage becomes positive. By inverting one input andconnecting two references to a level identical to the steady state (notsignal) level of the output of amplifier 44, the time comparator 60 willproduce a positive output when the level of amplifier 44 deviates fromthe no signal steady state level.

The output of dual comparator 60 is then connected through a diode 61which serves as a component of an OR gate (OR gate 18 in FIG. 1). Thus,a phase pickup circuit, such as the one shown in FIG. 2 and described tothis point, is provided for each current transformer which is monitoredin a circuit breaker system. Each. individual phase pickup circuit isconnected at its output through a diode, such as the diodes 62 and 63,which form an OR gate with the diode 61, so that an output signal isproduced if current flow is monitored in any phase of the breaker.

The output of the OR circuit, as shown in dotted lines in FIG. 2, isthen connected through the a breaker contact of the breaker in questionand the output of the a breaker contact is connected to ground throughresistors 71 and 72. Note that the outputs of other a breaker contactsof other breakers which are to be monitored by a common relay will alsobe connected to resistors 71 and 72 of FIG. 2. v

The output from the a breaker contact 70 is then coupled to theamplifier defined by transistor 73 (amplifier 24 of FIG. 1). Capacitor74 connects the collector of transistor 73 to ground, thereby to filterthe input applied to the base of transistor 75, which defines a secondamplifier. Note that the filter circuit, including capacitor 74, isshown as filter 25 in FIG. 1 while the amplifier including transistor 75is shown as amplifier 26 in FIG. 1.

The capacitor 74 of FIG. 2 provides continuity of the timing cycleduring zero crossing of the a-c input signal. The transistor 73 is sobiased that it is normally off, but is turned on due to a signal fromany phase pickup circuit. Transistor 75 is so biased that it normallyconducts but is turned off in response to the conduction of transistor73.

When transistor 75 normally conducts, it shorts out the timing capacitor76 of the timing circuit. This timing circuit (equivalent to timingcircuit 27 of FIG. 1) includes capacitor 76, resistor 77 and adjustableresistor 78 which can be used to adjust the time delay required beforethe relay of the invention will trip. Thus, with the appearance of asignal following the instant of opening of any of the interrupters beingmonitored, the transistor 75 turns off and capacitor 76 begins tocharge, thereby to begin to measure the length of time that the signaloutput from the a breaker contacts continues to exist.

The output of the capacitor 76 is then connected to a Schmidt triggercircuit, which monitors the voltage across capacitor 76. This Schmidttrigger includes transistors 80 and 81 and operates such that the relayoutput at terminal 82 switches positive when the capacitor voltage atterminal 83 exceeds some preset value.

The output of the Schmidt trigger of FIG. 2 may then be suitablyconnected to any output circuit which can include a trip circuit fortripping backup breakers or for activating an alarm circuit.

It will be understood that the novel circuit of the present inventionallows the timing of the length of time that the arc current flows afterinterrupter contacts open. Thus, when the main interrupter contactsopen, the a breaker contacts close, so that a signal is produced topermit the charging of capacitor 76 so long as arcing current flowsbetween the open contacts. Once the arcing current is extinguished, thesignal at dual comparator 60 is switched off so that transistor 73 isturned off and transistor 75 is turned on to disable the timing circuitand to prevent the production of a voltage at terminal 83 which canswitch the Schmidt trigger and cause the production of an output signal.However, if, due to a faulty vacuum, arc current flows too long in anyphase, the Schmidt trigger will switch to produce an alarm or the like.In a similar manner, if leakage current beyond some given level beginsto flow while the circuit breaker contacts are open, an output warningsignal will ultimately be developed after a given time delay.

FIG. 3 shows a modified phase pickup circuit arrangement, as compared tothe phase pickup circuit of FIG. 2, wherein the fault current protectionportion of the circuit has been changed. Thus, in FIG. 3, all componentssimilar to those in FIG. 2 have been given similar numerals. The phasepickup circuit of FIG. 3 has a modified connection for transistors 47and 48 and adds a zener diode 90, connected between the emitters oftransistors 47 and 48 and ground. In addition, the bases of transistors47 and 48 are connected together and to their collector electrodes andthe bias resistors 49, 50 and 52 of FIG. 2 have been removed.

The fault-current protection circuit of FIG. 3 has greater accuracy thanthat of FIG. 2 in its protection function. In the circuit of FIG. 3, thebias level set by resistors 45 and 46 is the same as the zener voltageacross the zener diode 90. This arrangement limits the voltage excursionat the input of operational amplifier 44 to the base-emitter junctiondrops of transistors 47 and 48. That is, when the input voltage atterminal 40 tends to exceed the junction voltage drop of transistor 48,transistor 48 conducts and provides the desired protection. Similarly,if the input voltage falls below the junction drop of transistor 47,then transistor 47 conducts to provide the desired protection. Note thatin the circuit of FIG. 3, as contrasted to the circuit of FIG. 2, theemitter voltage is held constant for the transistors 47 and 48.

Although the present invention has been described in connection with apreferred embodiment thereof, many variations and modifications will nowbecome apparent to those skilled in the art. It is preferred, therefore,that the present invention be limited not by the specific disclosureherein, but only by the appended claims.

The embodiments of the invention in which an exclusive privilege orproperty is claimed are defined as follows:

1. An arcing time relay for a circuit breaker; said circuit breakerincluding at least one interrupter having a pair of separable contacts,a current monitor means for monitoring current flow through said pair ofseparable contacts and contact means which are closed when said pair ofseparable contacts are opened, and which are opened when said pair ofseparable contacts are closed; said arcing time relay including:

a. a phase pickup circuit connected to said current monitor means andproducing an output current in response to the measurement of current inexcess of a given magnitude by said current monitor means,

b. a time delay circuit having input means connectable to an inputcircuit and producing a given output after an input current is connectedto its said input means for longer than a given time,

c. circuit means connecting said output current of said phase pickupcircuit to said input means of said time delay circuit through saidcontact means,

(I. and output circuit means connected to the output of said time delaycircuit and operable in response to said given output of said time delaycircuit, wherein said given output is produced only in response tocurrent flow through said pair of separable contacts after saidseparable contacts are opened.

2. The relay of claim 1 wherein said circuit breaker contains aplurality of interrupter phases and a corresponding plurality of phasepickup circuits identical to said phase pickup circuit, one for each ofsaid phases; the output current of each of said plurality of phasepickup circuits being connected to said input means.

3. The relay of claim 1 wherein said circuit breaker contains aplurality of interrupter phases and a corresponding plurality of pickupcircuits identical to said phase pickup circuit, one for each of saidphases; the output current of each of said plurality of phase pickupcircuits being connected to said input means, and wherein there is aplurality of circuits breakers of identical construction to said circuitbreaker; each of the phases of each of said plurality of circuitsbreakers containing respective phase pickup circuits; the contact meansof each of said plurality of circuit breakers connected in parallel,whereby excessive arcing current in any phase of any of said pluralityof circuit breakers causes the production of said given output by saidtime delay circuit.

4. The relay of claim 1 wherein said interrupter is a vacuuminterrupter.

5. The relay of claim 1 which further includes fault current protectioncircuit means connected between said current monitor means and saidphase pickup circuit for preventing the application of excessive signalsto said phase pickup circuit produced by fault current through said pairof separable contacts.

6. The relay of claim 1 which further includes fault current protectioncircuit means connected between said current monitor means and saidphase pickup circuit for preventing the application of excessive signalsto said phase pickup circuit produced by fault current through said pairof separable contacts, and wherein said phase pickup circuit includesoperational amplifier means coupled to said current monitor meansthrough said fault current protection circuit means, and a dualcomparator circuit means coupled to said operational amplifier means forproducing an output signal from said phase pickup circuit when theoutput of said operational amplifier means deviates from a given steadystate level.

7. The arcing time relay of claim 1 wherein said output circuit meansincludes a Schmidt trigger circuit which is switched in response to saidtime delay circuit producing said given value and which further includesalarm circuit means actuated by the switching of said Schmidt triggercircuit.

8. The relay of claim 6 wherein said interrupter is a vacuuminterrupter.

9. The relay of claim 8 wherein said circuit breaker contains aplurality of interrupter phases and a corresponding plurality of pickupcircuits identical to said phase pickup circuit, one for each of saidphases; the output current of each of said plurality of phase pickupcircuits being connected to said input means.

10. The arcing time relay of claim 8 wherein said output circuit meansincludes a Schmidt trigger circuit which is switched in response to saidtime delay circuit producing said given value and which further includesalarm circuit means actuated by the switching of said Schmidt triggercircuit.

1. An arcing time relay for a circuit breaker; said circuit breaker including at least one interrupter having a pair of separable contacts, a current monitor means for monitoring current flow through said pair of separable contacts and contact means which are closed when said pair of separable contacts are opened, and which are opened when said pair of separable contacts are closed; said arcing time relay including: a. a phase pickup circuit connected to said current monitor means and producing an output current in response to the measurement of current in excess of a given magnitude by said current monitor means, b. a time delay circuit having input means connectable to an input circuit and producing a given output after an input current is connected to its said input means for longer than a given time, c. circuit means connecting said output current of said phase pickup circuit to said input means of said time delay circuit through said contact means, d. and output circuit means connected to the output of said time delay circuit and operable in response to said given output of said time delay circuit, wherein said given output is produced only in response to current flow through said pair of separable contacts after said separable contacts are opened.
 2. The relay of claim 1 wherein said circuit breaker contains a plurality of interrupter phases and a corresponding plurality of phase pickup circuits identical to said phase pickup circuit, one for each of said phases; the output current of each of said plurality of phase pickup circuiTs being connected to said input means.
 3. The relay of claim 1 wherein said circuit breaker contains a plurality of interrupter phases and a corresponding plurality of pickup circuits identical to said phase pickup circuit, one for each of said phases; the output current of each of said plurality of phase pickup circuits being connected to said input means, and wherein there is a plurality of circuits breakers of identical construction to said circuit breaker; each of the phases of each of said plurality of circuits breakers containing respective phase pickup circuits; the contact means of each of said plurality of circuit breakers connected in parallel, whereby excessive arcing current in any phase of any of said plurality of circuit breakers causes the production of said given output by said time delay circuit.
 4. The relay of claim 1 wherein said interrupter is a vacuum interrupter.
 5. The relay of claim 1 which further includes fault current protection circuit means connected between said current monitor means and said phase pickup circuit for preventing the application of excessive signals to said phase pickup circuit produced by fault current through said pair of separable contacts.
 6. The relay of claim 1 which further includes fault current protection circuit means connected between said current monitor means and said phase pickup circuit for preventing the application of excessive signals to said phase pickup circuit produced by fault current through said pair of separable contacts, and wherein said phase pickup circuit includes operational amplifier means coupled to said current monitor means through said fault current protection circuit means, and a dual comparator circuit means coupled to said operational amplifier means for producing an output signal from said phase pickup circuit when the output of said operational amplifier means deviates from a given steady state level.
 7. The arcing time relay of claim 1 wherein said output circuit means includes a Schmidt trigger circuit which is switched in response to said time delay circuit producing said given value and which further includes alarm circuit means actuated by the switching of said Schmidt trigger circuit.
 8. The relay of claim 6 wherein said interrupter is a vacuum interrupter.
 9. The relay of claim 8 wherein said circuit breaker contains a plurality of interrupter phases and a corresponding plurality of pickup circuits identical to said phase pickup circuit, one for each of said phases; the output current of each of said plurality of phase pickup circuits being connected to said input means.
 10. The arcing time relay of claim 8 wherein said output circuit means includes a Schmidt trigger circuit which is switched in response to said time delay circuit producing said given value and which further includes alarm circuit means actuated by the switching of said Schmidt trigger circuit. 